The purpose of this study is to assess the efficacy, of treating patients with recurrent glioblastoma using Gamma-Knife Radiosurgery (GKS) to target a tumor volume defined by a combination of gadolinium enhancement and magnetic resonance spectroscopy (MRS). This is a single center, Phase II trial. A total of 40 glioblastoma patients will be enrolled into the primary arm of the trial. In addition, a minimum of 10 patients with recurrent anaplastic (grade III) gliomas and a minimum of 10 patients with recurrent low-grade (grade II) gliomas will be enrolled into exploratory arms.